Display device and method for self-assembling semiconductor light emitting diodes

ABSTRACT

A display device can include a plurality of semiconductor light emitting diodes; first and second wiring electrodes respectively extending from the plurality of semiconductor light emitting diodes to supply an electrical signal to the plurality of semiconductor light emitting diodes; a plurality of pair electrodes disposed on a substrate and having a first electrode and a second electrode that generate an electric field when a current is supplied thereto; a dielectric layer disposed to cover the plurality of pair electrodes; and a covalent bond layer disposed between the dielectric layer and the plurality of semiconductor light emitting diodes, and forming a covalent bond with the dielectric layer and each of the plurality of semiconductor light emitting diodes, wherein the first wiring electrode and the second wiring electrode are located at opposite sides of the plurality of pair electrodes based on the plurality of semiconductor light emitting diodes.

CROSS-REFERENCE TO RELATED APPLICATION

Pursuant to 35 U.S.C. § 119(a), this application claims the benefit ofthe earlier filing date and the right of priority to Korean PatentApplication No. 10-2019-0073654, filed in the Republic of Korea on Jun.20, 2019, the entire contents of which is hereby expressly incorporatedby reference into the present application.

BACKGROUND 1. Technical Field

The present disclosure relates to a display device and a method ofself-assembling semiconductor light emitting diodes for manufacturingthe display device, and one particular implementation relates to adisplay device using semiconductor light emitting diodes having sizes ofseveral μm to several tens of μm and a method of manufacturing the same.

2. Description of the Related Art

In recent years, in the field of display technology, liquid-crystaldisplays (LCD), organic light-emitting diode (OLED) displays, microLEDdisplays, etc. have been competing to realize large-area displays.

Meanwhile, semiconductor microLEDs (μLED) with a diameter orcross-sectional area less than 100 microns, when used in displays, canoffer very high efficiency because the displays do not need a polarizerto absorb light. However, large-scale displays require several millionsof semiconductor light-emitting diodes, which makes it difficult totransfer the devices compared to other technologies.

Some of the technologies currently in development for the transferprocess include pick & place, laser lift-off (LLO), and self-assembly.Among these technologies, the self-assembly approach is a method thatallows semiconductor light-emitting diodes to find their positions ontheir own in a fluid, which is most advantageous in realizinglarge-screen display devices.

Recently, U.S. Pat. No. 9,825,202 disclosed a microLED structuresuitable for self-assembly, but there is not enough research beingcarried out on technologies for manufacturing displays by theself-assembly of microLEDs. In view of this, the present disclosureproposes a new manufacturing method and device for self-assemblingmicroLEDs.

SUMMARY OF THE INVENTION

One aspect of the present disclosure is to provide a new manufacturingprocess that provides high reliability in large-screen displays usingmicro-size semiconductor light-emitting diodes.

Another aspect of the present disclosure is to provide a manufacturingprocess, capable of improving transfer accuracy when self-assemblingsemiconductor light-emitting diodes onto an assembly substrate.

Still another aspect of the present disclosure is to provide astructure, which can prevent semiconductor light emitting diodes frombeing separated from a substrate after the semiconductor light emittingdiodes are self-assembled, and a method for manufacturing the same.

To achieve these and other advantages and in accordance with the purposeof this specification, as embodied and broadly described herein, thereis provided a display device, including a plurality of semiconductorlight emitting diodes, first and second wiring electrodes respectivelyextending from the semiconductor light emitting diodes to supply anelectrical signal to the semiconductor light emitting diodes, aplurality of pair electrodes disposed on a substrate and having a firstelectrode and a second electrode that generate an electric field when acurrent is supplied, and a dielectric layer disposed to cover the pairelectrodes. The first wiring electrode and the second wiring electrodecan be located at an opposite side of the plurality of pair electrodesbased on the semiconductor light emitting diodes. The display device canfurther include a covalent bond layer disposed between the dielectriclayer and the semiconductor light emitting diodes and forming a covalentbond with the dielectric layer and each of the semiconductor lightemitting diodes.

In one embodiment, an Si—O bond can be formed between the dielectriclayer and the covalent bond layer.

In one embodiment, any one of an ester bond and an amide bond can beformed between the semiconductor light emitting diode and the covalentbond layer.

In one embodiment, the covalent bond layer can be a reaction productbetween a functional group formed on a surface of the substrate and asurface of each of the semiconductor light emitting diodes and acompound according to the following chemical formula 3, or a reactionproduct between the functional group formed on the surface of thesubstrate and the surface of each of the semiconductor light emittingdiodes and a mixture of the compound according to the following chemicalformula 3 and a compound according to the following chemical formula 4,

A method for self-assembling semiconductor light emitting diodesaccording to the present disclosure can include forming predeterminedfunctional groups on surfaces of a plurality of semiconductor lightemitting diodes each including a magnetic material, through surfacetreatment, bonding a predetermined compound to a surface of a substratehaving a plurality of assembly electrodes, transferring the substrate toan assembly position and introducing the semiconductor light emittingdiodes into a fluid chamber, applying magnetic force to thesemiconductor light-emitting diodes so that the semiconductorlight-emitting diodes move in one direction within the fluid chamber,inducing the semiconductor light emitting diodes to a preset position byapplying a voltage to the plurality of assembly electrodes disposed onthe substrate, such that the semiconductor light emitting diodes areseated at the preset position during the movement, and performing heattreatment for the substrate such that a covalent bond is formed througha reaction between the predetermined functional groups and thepredetermined compound bonded to the surface of the substrate.

In one embodiment, the applying of the magnetic force to thesemiconductor light emitting diodes and the inducing of thesemiconductor light emitting diodes to the preset position can beperformed at least once in a state where semiconductor light emittingdiodes emitting a first color are introduced into the fluid chamber, andat least once in a state where semiconductor light emitting diodesemitting a second color different from the first color are introduced inthe fluid chamber.

In one embodiment, the inducing of the semiconductor light emittingdiodes emitting the first color to the preset position can be performedby applying a voltage to a part of the plurality of assembly electrodesso that the semiconductor light emitting diodes emitting the first colorare induced to a preset first position, the inducing of thesemiconductor light emitting diodes emitting the second color to thepreset position can be performed by applying a voltage to another partof the plurality of assembly electrodes so that the semiconductor lightemitting diodes emitting the second color are induced to a preset secondposition.

In one embodiment, the performing of the heat treatment of the substratecan be performed at least once in the state where the semiconductorlight emitting diodes emitting the first color are seated at the presetfirst position, and at least once in the state where the semiconductorlight emitting diodes emitting the second color are seated at the presetsecond position.

The method can further include blocking a voltage applied to a part ofthe plurality of assembly electrodes when the semiconductor lightemitting diodes emitting the second color are induced to the presetsecond position after the semiconductor light emitting diodes emittingthe first color are seated in the preset first position.

In one embodiment, the preset compound can be a compound according tothe following chemical formula 3, or a mixture of a compound accordingto the following chemical formula 3 and a compound according to thefollowing chemical formula 4,

With the above configuration according to the present disclosure, manysemiconductor light-emitting diodes can be assembled at a time on adisplay device where individual pixels are made up of microLEDs.

As such, according to the present disclosure, a large number ofsemiconductor light-emitting diodes can be pixelated on a small-sizedwafer and then transferred onto a large-area substrate. This enables themanufacture of a large-area display device at a low cost.

Moreover, according to the manufacturing method of the presentdisclosure, a low-cost, high-efficiency, and quick transfer ofsemiconductor light-emitting diodes can be done, regardless of the sizesor numbers of parts and the transfer area, by simultaneouslytransferring them in the right positions in a solution by using amagnetic field and an electric field.

Furthermore, the assembling of semiconductor light-emitting diodes by anelectric field allows for selective assembling through selectiveelectrical application without any additional equipment or processes.Also, since an assembly substrate is placed on top of a chamber, thesubstrate can be easily loaded or unloaded, and non-specific binding ofsemiconductor light-emitting diodes can be prevented.

According to the present disclosure, in the case of sequentiallyself-assembling different types of semiconductor light emitting diodes,when semiconductor light emitting diodes of another type areself-assembled after semiconductor light emitting diodes of one type areself-assembled, a voltage applied to the assembly electrodescorresponding to the one type of semiconductor light emitting diodes canbe blocked by use of the covalent bond layer. Accordingly, the presentdisclosure can prevent the semiconductor light emitting diodes of theanother type from being aligned at a position where the semiconductorlight emitting diodes of the one type should be aligned, in the casewhere such different types of semiconductor light emitting diodes aresequentially self-assembled.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual view illustrating one embodiment of a displaydevice using a semiconductor light emitting diode according to thepresent disclosure.

FIG. 2 is a partial enlarged view of the portion A in the display deviceof FIG. 1.

FIG. 3 is an enlarged view of the semiconductor light-emitting diodes ofFIG. 2.

FIG. 4 is an enlarged view illustrating another embodiment of thesemiconductor light-emitting diodes of FIG. 2.

FIGS. 5A to 5E are conceptual diagrams for explaining a new process formanufacturing the above-described semiconductor light-emitting diodes.

FIG. 6 is a conceptual diagram illustrating an example of a device forself-assembling semiconductor light-emitting diodes according to thepresent disclosure.

FIG. 7 is a block diagram of the self-assembly device of FIG. 6.

FIGS. 8A to 8E are conceptual diagrams illustrating a process forself-assembling semiconductor light-emitting diodes using theself-assembly device of FIG. 6.

FIG. 9 is a conceptual diagram illustrating the semiconductorlight-emitting diodes of FIGS. 8A to 8E.

FIG. 10 is a conceptual diagram illustrating a surface treatment methodfor a semiconductor light emitting diode.

FIG. 11 is a conceptual diagram illustrating a surface treatment methodapplied to a substrate.

FIGS. 12 and 13 are conceptual diagrams illustrating formation of acovalent bond layer through an ester reaction.

FIGS. 14 and 15 are conceptual diagrams illustrating formation of acovalent bond layer through an amide reaction.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Description will now be given in detail according to exemplaryembodiments disclosed herein, with reference to the accompanyingdrawings. For the sake of brief description with reference to thedrawings, the same or equivalent components can be provided with thesame or similar reference numbers, and description thereof will not berepeated. In general, a suffix such as “module” and “unit” can be usedto refer to elements or components. Use of such a suffix herein ismerely intended to facilitate description of the specification, and thesuffix itself is not intended to give any special meaning or function.In describing the present disclosure, if a detailed explanation for arelated known function or construction is considered to unnecessarilydivert the gist of the present disclosure, such explanation has beenomitted but would be understood by those skilled in the art. Theaccompanying drawings are used to help easily understand the technicalidea of the present disclosure and it should be understood that the ideaof the present disclosure is not limited by the accompanying drawings.

It will be understood that when an element such as a layer, area orsubstrate is referred to as being “on” another element, it can bedirectly on the element, or one or more intervening elements can also bepresent.

A display device disclosed herein can include a portable phone, a smartphone, a laptop computer, a digital broadcast terminal, a personaldigital assistant (PDA), a portable multimedia player (PMP), anavigation, a slate PC, a tablet PC, an ultrabook, a digital TV, adigital signage, a head mounted display (HMD), a desktop computer, andthe like. However, it will be readily apparent to those skilled in theart that the configuration according to the embodiments described hereincan also be applied to a new product type that will be developed laterif the device is a device capable of emitting light.

FIG. 1 is a conceptual diagram illustrating one embodiment of a displaydevice using semiconductor light-emitting diodes according to thepresent disclosure, FIG. 2 is a partial enlarged view of the portion Ain the display device of FIG. 1, FIG. 3 is an enlarged view of thesemiconductor light-emitting diodes of FIG. 2, and FIG. 4 is an enlargedview illustrating another embodiment of the semiconductor light-emittingdiodes of FIG. 2. All elements of the display device are operationallycoupled and configured.

According to the illustration, information processed by a controller ofa display device 100 can be output by a display module 140. A closedloop-shaped case 101 that runs around the edge of the display module canform the bezel of the display device.

The display module 140 comes with a panel 141 that displays an image,and the panel 141 can come with micro-sized semiconductor light-emittingdiodes 150 and a wiring substrate 110 where the semiconductorlight-emitting diodes 150 are mounted.

The wiring substrate 110 can be formed with wiring lines or wiringelectrodes including first and second wiring electrodes, which can beconnected to n-type electrodes 152 and p-type electrodes 156 of thesemiconductor light-emitting diodes 150. As such, the semiconductorlight-emitting diodes 150 can be provided on the wiring substrate 110 asindividual pixels that emit light on their own.

The image displayed on the panel 141 is visual information, which isrendered by controlling the light emission of unit pixels (sub-pixels)arranged in a matrix independently through the wiring lines.

The present disclosure takes microLEDs (light-emitting diodes) as anexample of the semiconductor light-emitting diodes 150 which convertcurrent into light. The microLEDs can be light-emitting diodes that aresmall in size—less than 100 microns. The semiconductor light-emittingdiodes 150 have light-emitting regions of red, green, and blue, and unitpixels can produce light through combinations of these colors. That is,the unit pixels are the smallest units for producing one color. Eachunit pixel can contain at least three microLEDs.

More specifically, referring to FIG. 3, the semiconductor light-emittingdiode 150 can have a vertical structure.

For example, the semiconductor light-emitting diodes 150 can beimplemented as high-power light-emitting diodes that are composed mostlyof gallium nitride (GaN), with some indium (In) and/or aluminum (Al)added to it, and emit light of various colors.

Such a vertical semiconductor light-emitting diode comprises a p-typeelectrode 156, a p-type semiconductor layer 155 formed on the p-typesemiconductor layer 156, an active layer 154 formed on the p-typesemiconductor layer 155, an n-type semiconductor layer 153 formed on theactive layer 154, and an n-type electrode 152 formed on the n-typesemiconductor layer 153. In this case, the p-type electrode 156 at thebottom can be electrically connected to a p electrode of the wiringsubstrate, and the n-type electrode 152 at the top can be electricallyconnected to an n electrode above the semiconductor light-emittingdiode. The electrodes can be disposed in the upward/downward directionin the vertical semiconductor light-emitting diode 150, therebyproviding a great advantage capable of reducing the chip size.

In another example, referring to FIG. 4, the semiconductorlight-emitting diodes can be flip chip-type light-emitting diodes.

As an example of such a flip chip-type light-emitting diode, thesemiconductor light-emitting diode 250 comprises a p-type electrode 256,a p-type semiconductor layer 255 formed on the p-type semiconductorlayer 256, an active layer 254 formed on the p-type semiconductor layer255, an n-type semiconductor layer 253 formed on the active layer 254,and an n-type electrode 252 vertically separated from the p-typeelectrode 256, on the n-type semiconductor layer 253. In this case, boththe p-type electrode 256 and the n-type electrode 252 can beelectrically connected to a p electrode and n electrode of the wiringsubstrate, below the semiconductor light-emitting diode.

The vertical semiconductor light-emitting diode and a horizontallight-emitting diode each can be used as a green semiconductorlight-emitting diode, blue semiconductor light-emitting diode, or redsemiconductor light-emitting diode. The green semiconductorlight-emitting diode and the blue semiconductor light-emitting diode canbe implemented as high-power light-emitting diodes that are composedmostly of gallium nitride (GaN), with some indium (In) and/or aluminum(Al) added to it, and emit green and blue light, respectively. As anexample of such high-power light-emitting diodes, the semiconductorlight-emitting diodes can be composed of gallium nitride thin filmswhich are formed of various layers of n-Gan, p-GaN, AlGaN, InGaN, etc.More specifically, the p-type semiconductor layer can be P-type GaN, andthe n-type semiconductor layer can be N-type GaN. However, for the redsemiconductor light-emitting diodes, the p-type semiconductor layer canbe P-type GaAs, and the n-type semiconductor layer can be N-type GaAs.

Moreover, the p-type semiconductor layer can be P-type GaN doped with Mgon the p electrode, and the n-type semiconductor layer can be N-type GaNdoped with Si on the n electrode. In this case, the above-describedsemiconductor light-emitting diodes can come without the active layer.

Meanwhile, referring to FIGS. 1 to 4, because of the very small size ofthe light-emitting diodes, self-emissive, high-definition unit pixelscan be arranged on the display panel, and therefore the display devicecan deliver high picture quality.

In the above-explained display device using semiconductor light-emittingdiodes according to the present disclosure, semiconductor light-emittingdiodes are grown on a wafer, formed through mesa and isolation, and usedas individual pixels. In this case, the micro-sized semiconductorlight-emitting diodes 150 should be transferred onto a wafer, at presetpositions on a substrate of the display panel. One of the transfertechnologies available is pick and place, but it has a low success rateand requires a lot of time. In another example, a number of diodes canbe transferred at a time by using a stamp or roll, which, however, isnot suitable for large-screen displays because of limited yields. Thepresent disclosure suggests a new method and device for manufacturing adisplay device that can solve these problems.

To this end, the new method for manufacturing a display device will bedescribed first below. FIGS. 5A to 5E are conceptual diagrams forexplaining a new process for manufacturing the above-describedsemiconductor light-emitting diodes.

In this specification, a display device using passive matrix (PM)semiconductor light-emitting diodes will be illustrated. It should benoted that the illustration given below also applies to active matrix(AM) semiconductor light-emitting diodes. Also, although theillustration will be given of how horizontal semiconductorlight-emitting diodes are self-assembled, it can also apply toself-assembling of vertical semiconductor light-emitting diodes.

First of all, according to the manufacturing method, a first conductivesemiconductor layer 153, an active layer 154, and a second conductivesemiconductor layer 155 are grown on a growth substrate 159 (FIG. 5A).

Once the first conductive semiconductor layer 153 is grown, then theactive layer 154 is grown on the first conductive semiconductor layer153, and then the second conductive semiconductor layer 155 is grown onthe active layer 154. By sequentially growing the first conductivesemiconductor layer 153, active layer 154, and second conductivesemiconductor layer 155, the first conductive semiconductor layer 153,active layer 154, and second conductive semiconductor layer 155 form astack structure as shown in FIG. 5A.

In this case, the first conductive semiconductor layer 153 can be ap-type semiconductor layer, and the second conductive semiconductorlayer 155 can be an n-type semiconductor layer. However, the presentdisclosure is not necessarily limited to this, and the first conductivetype can be n-type and the second conductive type can be p-type.

Moreover, although this exemplary embodiment is illustrated by assumingthe presence of the active layer, the active layer can be omitted ifnecessary, as stated above. In an example, the p-type semiconductorlayer can be P-type GaN doped with Mg, and the n-type semiconductorlayer can be N-type GaN doped with Si on the n electrode.

The growth substrate 159 (wafer) can be formed of, but not limited to,light-transmissive material—for example, at least one among sapphire(Al2O3), GaN, ZnO, and AlO. Also, the growth substrate 159 can be madefrom a material suitable for growing semiconductor materials or carrierwafer. The growth substrate 159 can be formed of a high thermalconducting material, and can be a conductive substrate or insulatingsubstrate—for example, at least one among SiC, Si, GaAs, GaP, InP, andGa2O3 substrates which have higher thermal conductivity than sapphire(Al2O3) substrates.

Next, a plurality of semiconductor light-emitting diodes is formed byremoving at least part of the first conductive semiconductor layer 153,active layer 154, and second conductive semiconductor layer 155 (FIG.5B).

More specifically, isolation is performed so that the light-emittingdiodes form a light-emitting diode array. That is, a plurality ofsemiconductor light-emitting diodes is formed by vertically etching thefirst conductive semiconductor layer 153, active layer 154, and secondconductive semiconductor layer 155.

In the case of horizontal semiconductor light-emitting diodes, a mesaprocess can be performed which exposes the first conductivesemiconductor layer 153 to the outside by vertically removing part ofthe active layer 154 and second conductive layer 155, and then isolationcan be performed which forms an array of semiconductor light-emittingdiodes by etching the first conductive semiconductor layer 153.

Next, a second conductive electrode 156 (or p-type electrode) is formedon one surface of the second conductive semiconductor layer 155 (FIG.5C). The second conductive electrode 156 can be formed by a depositionmethod such as sputtering, but the present disclosure is not necessarilylimited to this. In a case where the first conductive semiconductorlayer and the second conductive semiconductor layer are an n-typesemiconductor layer and a p-type semiconductor layer, respectively, thesecond conductive electrode 156 can serve as an n-type electrode.

Next, the growth substrate 159 is removed, thus leaving a plurality ofsemiconductor light-emitting diodes. For example, the growth substrate159 can be removed using laser lift-off (LLO) or chemical lift-off (CLO)(FIG. 5D).

Afterwards, the step of mounting the semiconductor light-emitting didoes150 on a substrate in a chamber filled with a fluid is performed (FIG.5E).

For example, the semiconductor light-emitting diodes 150 and thesubstrate are put into the chamber filled with a fluid, and thesemiconductor light-emitting diodes are self-assembled onto thesubstrate 1061 using fluidity, gravity, surface tension, etc. In thiscase, the substrate can be an assembly substrate 161.

In another example, a wiring substrate, instead of the assemblysubstrate 161, can be put into a fluid chamber, and the semiconductorlight-emitting diodes 150 can be mounted directly onto the wiringsubstrate. In this case, the substrate can be a wiring substrate. Forconvenience of explanation, the present disclosure is illustrated withan example in which the semiconductor light-emitting diodes 150 aremounted onto the assembly substrate 161.

To facilitate the mounting of the semiconductor light-emitting diodes150 onto the assembly substrate 161, cells into which the semiconductorlight-emitting diodes 150 are fitted can be provided on the assemblysubstrate 161. Specifically, cells where the semiconductorlight-emitting diodes 150 are mounted are formed on the assemblysubstrate 161, at positions where the semiconductor light-emittingdiodes 150 are aligned with wiring electrodes. The semiconductorlight-emitting diodes 150 are assembled to the cells as they move withinthe fluid.

After arraying the semiconductor light-emitting didoes on the assemblysubstrate 161, the semiconductor light-emitting diodes can betransferred to the wiring substrate from the assembly substrate 161,thereby enabling a large-area transfer across a large area. Thus, theassembly substrate 161 can be referred to as a temporary substrate.

Meanwhile, the above-explained self-assembly method requires a highertransfer yield so that it can be applied to the manufacture oflarge-screen displays. The present disclosure proposes a method anddevice that minimizes the effects of gravity or friction and avoidsnon-specific binding, in order to increase the transfer yield.

In this case, in the display device according to the present disclosure,a magnetic material is placed on the semiconductor light-emitting diodesso that the semiconductor light-emitting diodes are moved by magneticforce, and the semiconductor light-emitting diodes are mounted at presetpositions by an electric field while in the process of being moved. Thistransfer method and device will be described in more details below withreference to the accompanying drawings.

FIG. 6 is a conceptual diagram showing an example of a device forself-assembling semiconductor light-emitting diodes according to thepresent disclosure, and FIG. 7 is a block diagram of the self-assemblydevice of FIG. 6. FIGS. 8A to 8D are conceptual diagrams showing aprocess for self-assembling semiconductor light-emitting diodes usingthe self-assembly device of FIG. 6. FIG. 9 is a conceptual diagram forexplaining the semiconductor light-emitting diodes of FIGS. 8A to 8D.All elements of the device for self-assembling semiconductorlight-emitting diodes according to the present disclosure areoperationally coupled and configured.

Referring to FIGS. 6 and 7, the self-assembly device 160 of the presentdisclosure can comprise a fluid chamber 162, magnets 163, and a positioncontroller 164.

The fluid chamber 162 is equipped with space for a plurality ofsemiconductor light-emitting diodes. The space can be filled with afluid, and the fluid can be an assembly solution, which includes wateror the like. Thus, the fluid chamber 162 can be a water tank andconfigured as open-type. However, the present disclosure is not limitedto this, and the fluid chamber 162 can be a closed-type chamber thatcomes with a closed space.

A substrate 161 can be placed in the fluid chamber 162 so that anassembly surface where the semiconductor light-emitting diodes 150 areassembled faces downwards. For example, the substrate 161 is fed to anassembly site by a feed unit, and the feed unit can come with a stage165 where the substrate is mounted. The position of the stage 165 can beadjusted by the controller, whereby the substrate 161 can be fed to theassembly site.

In this instance, the assembly surface of the substrate 161 at theassembly site faces the bottom of the fluid chamber 162. As shown in thedrawings, the assembly surface of the substrate 161 is placed in such away as to be soaked with the fluid in the fluid chamber 162. Thus, thesemiconductor light-emitting diodes 150 in the fluid are moved to theassembly surface.

The substrate 161 is an assembly substrate where an electric field canbe formed, and can comprise a base portion 161 a, a dielectric layer 161b, and a plurality of electrodes 161 c.

The base portion 161 a is made of insulating material, and theelectrodes 161 c can be thin-film or thick-film bi-planar electrodesthat are patterned on one surface of the base portion 161 a. Theelectrodes 161 c can be formed of a stack of Ti/Cu/Ti, Ag paste, ITO,etc.

The dielectric layer 161 b can be made of inorganic material such asSiO₂, SiN_(X), SiON, Al₂O₃, TiO₂, HfO₂, etc. Alternatively, thedielectric layer 161 b can be an organic insulator and composed of asingle layer or multi-layers. The thickness of the dielectric layer 161b can range from several tens of nm to several μm.

Further, the substrate 161 according to the present disclosure comprisesa plurality of cells 161 d that are separated by barrier walls 161 e.The cells 161 d can be sequentially arranged in one direction and madeof polymer material. Also, the barrier walls 161 e forming the cells 161d can be shared with neighboring cells 161 d. The barrier walls 161 ecan protrude from the base portion 161 a, and the cells 161 d can besequentially arranged in one direction along the barrier walls 161 e.More specifically, the cells 161 d can be sequentially arranged incolumn and row directions and have a matrix structure.

As shown in the drawings, the cells 161 d can have recesses forcontaining the semiconductor light-emitting diodes 150, and the recessescan be spaces defined by the barrier walls 161 e. The recesses can havea shape identical or similar to the shape of the semiconductorlight-emitting diodes. For example, if the semiconductor light-emittingdiodes are rectangular, the recesses can be rectangular too. Moreover,the recesses formed in the cells can be circular if the semiconductorlight-emitting diodes are circular. Further, each cell is configured tocontain one semiconductor light-emitting diode. That is, one cellcontains one semiconductor light-emitting diode.

Meanwhile, the plurality of electrodes 161 c have a plurality ofelectrode lines that are placed at the bottom of the cells 161 d, andthe electrode lines can be configured to extend to neighboring cells.

The electrodes 161 c are placed on the undersides of the cells 161 d,and different polarities can be applied to create an electric fieldwithin the cells 161 d. To form an electric field, the dielectric layer161 b can form the bottom of the cells 161 d while covering theelectrodes 161 c. With this structure, when different polarities areapplied to a pair of electrodes 161 c on the underside of each cell 161d, an electric field is formed and the semiconductor light-emittingdiodes can be inserted into the cells 161 d by the electric field.

The electrodes of the substrate 161 at the assembly site areelectrically connected to a power supply 171. The power supply 171performs the function of generating an electric field by applying powerto the electrodes.

As shown in the drawings, the self-assembly device can have magnets 163for applying magnetic force to the semiconductor light-emitting diodes.The magnets 163 are placed at a distance from the fluid chamber 162 andapply a magnetic force to the semiconductor light-emitting diodes 150.The magnets 163 can be placed to face the opposite side of the assemblysurface of the substrate 161, and the positions of the magnets 163 arecontrolled by the position controller 164 connected to the magnets 163.

The semiconductor light-emitting diodes 1050 can have a magneticmaterial so that they are moved within the fluid by a magnetic field.

Referring to FIG. 9, a semiconductor light-emitting diode having amagnetic material can comprise a first conductive electrode 1052, asecond conductive electrode 1056, a first conductive semiconductor layer1053 where the first conductive electrode 1052 is placed, a secondconductive semiconductor layer 1055 which overlaps the first conductivesemiconductor layer 1052 and where the second conductive layer 1056 isplaced, and an active layer 1054 placed between the first and secondconductive semiconductor layers 1053 and 1055.

Here, the first conductive can refer to p-type, and the secondconductive type can refer to n-type, or vice versa. As statedpreviously, the semiconductor light-emitting diode can be formed withoutthe active layer.

Meanwhile, in the present disclosure, the first conductive electrode1052 can be formed after the semiconductor light-emitting diode isassembled onto the wiring substrate by the self-assembling of thesemiconductor light-emitting diode. Further, in the present disclosure,the second conductive electrode 1056 can comprise a magnetic material.The magnetic material can refer a magnetic metal. The magnetic materialcan be Ni, SmCo, etc. In another example, the magnetic material caninclude at least one among Gd-based, La-based, and Mn-based materials.

The magnetic material can be provided in the form of particles on thesecond conductive electrode 1056. Alternatively, one layer of aconductive electrode comprising a magnetic material can be composed ofthe magnetic material. An example of this is the second conductiveelectrode 1056 of the semiconductor light-emitting diode 1050 whichcomprises a first layer 1056 a and a second layer 1056 b, as shown inFIG. 9. Here, the first layer 1056 a can comprise a magnetic material,and the second layer 1056 b can comprise a metal material other than themagnetic material.

As shown in the drawing, in this example, the first layer 1056 acomprising the magnetic material can be placed in contact with thesecond conductive semiconductor layer 1055. In this case, the firstlayer 1056 a is placed between the second layer 1056 b and the secondconductive semiconductor layer 1055. The second layer 1056 b can be acontact metal that is connected to the wiring electrode on the wiringsubstrate. However, the present disclosure is not necessarily limited tothis, and the magnetic material can be placed on one surface of thefirst conductive semiconductor layer.

Referring again to FIGS. 6 and 7, more specifically, on top of the fluidchamber of the self-assembly device, a magnet handler capable ofautomatically or manually moving the magnets 163 on the x, y, and z axesor a motor capable of rotating the magnets 163 can be provided. Themagnet handler and motor can constitute the position controller 164. Assuch, the magnets 163 can rotate in a horizontal, clockwise, orcounterclockwise direction to the substrate 161.

Meanwhile, the fluid chamber 162 can be formed with a light-transmissivebottom plate 166, and the semiconductor light-emitting diodes can beplaced between the bottom plate 166 and the substrate 161. An imagesensor 167 can be placed opposite the bottom plate 166 so as to monitorthe inside of the fluid chamber 162 through the bottom plate 166. Theimage sensor 167 can be controlled by a controller 172, and can comewith an inverted-type lens, CCD, etc. so as to observe the assemblysurface of the substrate 161.

The above-explained self-assembly device is configured to use a magneticfield and an electric field in combination. With this, the semiconductorlight-emitting diodes are mounted at preset positions on the substrateby an electric field while in the process of being moved by changes inthe positions of the magnets. Below, the assembly process using theabove-explained self-assembly device will be described in more details.

First of all, a plurality of semiconductor light-emitting diodes 1050having a magnetic material can be formed through the process explainedwith reference to FIGS. 5A to 5C. In this case, the magnetic materialcan be deposited onto the semiconductor light-emitting didoes in theprocess of forming the second conductive electrode of FIG. 5C.

Next, the substrate 161 is fed to an assembly site, and thesemiconductor light-emitting diodes 1050 are put into the fluid chamber162 (FIG. 8A).

As described above, the assembly site on the substrate 161 can be aposition at which the substrate 161 is placed in the fluid chamber 162in such a way that an assembly surface where the semiconductorlight-emitting diodes 150 are assembled faces downwards.

In this case, some of the semiconductor light-emitting diodes 1050 cansink to the bottom of the fluid chamber 162 and some of them can floatin the fluid. If the fluid chamber 162 comes with a light-transmissivebottom plate 166, some of the semiconductor light-emitting diodes 1050can sink to the bottom plate 166.

Next, a magnetic force is applied to the semiconductor light-emittingdiodes 1050 so that the semiconductor light-emitting diodes 1050 in thefluid chamber 162 come up to the surface (FIG. 8B).

When the magnets 163 of the self-assembly device move to the oppositeside of the assembly surface of the substrate 161 from their originalpositions, the semiconductor light-emitting diodes 1050 float in thefluid towards the substrate 161. The original positions can refer topositions at which the magnets 163 are outside the fluid chamber 162. Inanother example, the magnets 163 can be composed of electromagnets. Inthis case, an initial magnetic force is generated by supplyingelectricity to the electromagnets.

Meanwhile, in this embodiment, the spacing between the assembly surfaceof the substrate 161 and the semiconductor light-emitting diodes 1050can be controlled by adjusting the strength of the magnetic force. Forexample, the spacing is controlled by using the weight, buoyancy, andmagnetic force of the semiconductor light-emitting diodes 1050. Thespacing can be several millimeters to several tens of micrometers fromthe outermost part of the substrate 161.

Next, a magnetic force is applied to the semiconductor light-emittingdiodes 1050 so that the semiconductor light-emitting diodes 1050 move inone direction within the fluid chamber 162. For example, the magnets 163can move in a horizontal, clockwise, or counterclockwise direction tothe substrate 161 (FIG. 8C). In this case, the semiconductorlight-emitting diodes 1050 are moved horizontally to the substrate 161by the magnetic force, spaced apart from the substrate 161.

Next, the semiconductor light-emitting diodes 1050 are guided to presetpositions on the substrate 161 by applying an electric field so that thesemiconductor light-emitting diodes 1050 are mounted at the presetpositions while in the process of being moved (FIG. 8C). For example,the semiconductor light-emitting diodes 1050 are moved vertically to thesubstrate 161 by the electric field and mounted at preset positions onthe substrate 161, while being moved horizontally to the substrate 161.

More specifically, an electric field is generated by supplying power tobi-planar electrodes on the substrate 161, and the semiconductorlight-emitting diodes 1050 are guided to the preset positions andassembled only there by the electric field. That is, the semiconductorlight-emitting diodes 1050 are self-assembled at an assembly site on thesubstrate 161 by a selectively generated electric field. To this end,the substrate 161 can be formed with cells into which the semiconductorlight-emitting diodes 1050 are fitted.

Afterwards, the unloading of the substrate 161 is performed, therebycompleting the assembly process. In a case where the substrate 161 is anassembly substrate, an array of semiconductor light-emitting diodes canbe transferred onto a wiring substrate to carry out a subsequent processfor realizing the display device, as described previously.

Meanwhile, after the semiconductor light-emitting diodes 1050 are guidedto the preset positions, the magnets 163 can be moved in a direction inwhich they get farther away from the substrate 161, so that thesemiconductor light-emitting diodes 1050 remaining in the fluid chamber162 fall to the bottom of the fluid chamber 162 (FIG. 8D). In anotherexample, if power supply is stopped in a case where the magnets 163 areelectromagnets, the semiconductor light-emitting diodes 1050 remainingin the fluid chamber 162 fall to the bottom of the fluid chamber 162.

Thereafter, the semiconductor light-emitting diodes 1050 on the bottomof the fluid chamber 162 can be collected, and the collectedsemiconductor light-emitting diodes 1050 can be re-used.

In the above-explained self-assembly device and method, parts distantfrom one another are concentrated near a preset assembly site by using amagnetic field in order to increase assembly yields in a fluidicassembly, and the parts are selectively assembled only at the assemblysite by applying an electric field to the assembly site. In this case,the assembly substrate is positioned on top of a water tank, with itsassembly surface facing downward, thus minimizing the effect of gravityfrom the weights of the parts and avoiding non-specific binding andeliminating defects. That is, the assembly substrate is placed on thetop to increase transfer yields, thus minimizing the effect of gravityor friction and avoiding non-specific binding.

As seen from above, with the above configuration according to thepresent disclosure, large numbers of semiconductor light-emitting diodescan be assembled at a time on a display device where individual pixelsare made up of semiconductor light-emitting diodes.

As such, according to the present disclosure, large numbers ofsemiconductor light-emitting diodes can be pixelated on a small-sizedwafer and then transferred onto a large-area substrate. This enables themanufacture of a large-area display device at a low cost.

Meanwhile, as described with reference to FIGS. 8A to 8G, in theabove-described self-assembling method, semiconductor light emittingdiodes emitting different colors can be sequentially disposed on asubstrate. In order to arrange semiconductor light emitting diodesemitting different colors on a single substrate, a self-assembly processshould be performed as many as the number of types of the semiconductorlight emitting diodes. For example, the self-assembly process should beperformed at least three times to arrange semiconductor light emittingdiodes of emitting blue, red, and green on a single substrate.

In this specification, an embodiment of assembling semiconductor lightemitting diodes emitting three kinds of colors onto one substrate willbe described. However, types of semiconductor light emitting diodesassembled to one assembly substrate are not limited thereto.Hereinafter, semiconductor light emitting diodes emitting light ofdifferent colors will be referred to as first to third semiconductorlight emitting diodes, and the first to third semiconductor lightemitting diodes are sequentially assembled on an assembly substrate.

An electrode to which a voltage is applied varies depending on a type ofsemiconductor light emitting diode introduced or inserted into the fluidchamber. Hereinafter, the above-mentioned electrode 161 c is referred toas an assembly electrode. Specifically, a plurality of assemblyelectrodes 161 c is divided into three groups. Hereinafter, theplurality of assembly electrodes is divided into first to third groups.

In the self-assembly, the first semiconductor light emitting diodesoverlap any one of the assembly electrodes belonging to the first group.The second semiconductor light emitting diodes overlap any one of theassembly electrodes belonging to the second group. The thirdsemiconductor light emitting diodes overlap any one of the assemblyelectrodes belonging to the third group.

When the self-assembly is performed while the first semiconductor lightemitting diodes are introduced into the fluid chamber, a voltage must beapplied to the assembly electrodes belonging to the first group. Whenthe self-assembly is performed while the second semiconductor lightemitting diodes are introduced into the fluid chamber, a voltage must beapplied to the assembly electrodes belonging to the second group. Also,when the self-assembly is performed while the third semiconductor lightemitting diodes are introduced into the fluid chamber, a voltage must beapplied to the assembly electrodes belonging to the third group.

However, a voltage is not required to be applied only to assemblyelectrodes of a group corresponding to specific semiconductor lightemitting diodes in a state in which the specific semiconductor lightemitting diodes are introduced in the fluid chamber. Specifically, whenthe self-assembly is performed while the second semiconductor lightemitting diodes are introduced in the fluid chamber, the firstsemiconductor light emitting diodes have already been bonded to thesubstrate. In this instance, when a voltage applied to the assemblyelectrodes belonging to the first group is blocked, the firstsemiconductor light emitting diodes can be separated from the substrate.In order to prevent this, when the self-assembly is performed while thesecond semiconductor light emitting diodes are introduced, a voltagemust be applied to both the first and second groups. In this instance,attractive force can act between the assembly electrodes belonging tothe first group and the second semiconductor light emitting diodes.However, since the first semiconductor light emitting diodes are alreadyaligned at designated positions, the second semiconductor light emittingdiodes are not aligned to overlap the assembly electrodes belonging tothe first group.

On the other hand, when the third semiconductor light emitting diodesare self-assembled, a voltage must be applied to all of the first tothird groups in the state in which the third semiconductor lightemitting diodes are introduced in the fluid chamber.

However, in the above-described self-assembly method, when asemiconductor light emitting diode is not seated (mounted, placed,aligned) at a preset position during self-assembly, a problem arises inthat an unwanted semiconductor light emitting diode is seated at thepreset position in a subsequent self-assembly process.

For example, when the first semiconductor light emitting diodes arecompletely self-assembled, the first semiconductor light emitting diodesmay not be mounted in some grooves overlapping with the assemblyelectrodes belonging to the first group. In this state, when theself-assembly for the second semiconductor light emitting diodes isperformed, the second semiconductor light emitting diodes can be mountedon positions where the first semiconductor light emitting diodes shouldbe placed. This is because a voltage is applied to the assemblyelectrodes belonging to the first group even during the self-assemblyfor the second semiconductor light emitting diodes. In order to preventseparation of the pre-assembled first semiconductor light emittingdiodes, it is inevitable to apply a voltage to the assembly electrodesbelonging to the first group even during the self-assembly for thesecond semiconductor light emitting diodes. However, this causes aproblem in that the semiconductor light emitting diodes are incorrectlyassembled.

The present disclosure provides a structure and method for blocking avoltage applied to an assembly electrode, which has formed an electricfield during a preceding self-assembly, when a subsequent self-assemblyis performed after the completion of the preceding self-assembly.

Hereinafter, a self-assembly method according to the present disclosurewill be described.

First, a step of forming through surface treatment predeterminedfunctional groups on surfaces of a plurality of semiconductor lightemitting diodes each having a magnetic material is performed.

Specifically, functional groups are formed on the surfaces of thesemiconductor light emitting diodes in a state in which thesemiconductor light emitting diodes are separated from a growthsubstrate. Hydrophilic functional groups can be formed on the surfacesof the semiconductor light emitting diodes. For example, at least one ofa hydroxyl group and an amine group can be formed on the surfaces of thesemiconductor light emitting diodes. However, the present disclosure isnot limited thereto, and the functional group can be any functionalgroup capable of forming a covalent bond through a condensationreaction.

In one embodiment, referring to FIG. 10, when the semiconductor lightemitting diodes 350 (or 350″) are subjected to O2-plasma treatment(e.g., 50 W) for about 2 minutes, for example, and followed by surfacetreatment for 8 hours in a 80° C. solution that 2% of aminopropyltrimethoxysilane (APTMS) is dissolved in EtOH (99.5%), an amine group isformed on the surfaces of the semiconductor light emitting diodes 350′.

Here, the structure of APTMS is shown in the following chemical formula(1).

On the other hand, a compound for the surface treatment of thesemiconductor light emitting diodes is not limited to APTMS. In anotherembodiment, the surfaces of the semiconductor light emitting diodes canbe treated with a compound (glycidoxypropyl trimethoxysilane (GPTMS))according to the following chemical formula (2).

In another embodiment, when the O2-plasma treatment (e.g., 50 W) isperformed on the semiconductor light emitting diodes for about 2minutes, a large amount of hydroxyl groups is produced on the surfacesof the semiconductor light emitting diodes.

The functional group formed on the surfaces of the semiconductor lightemitting diodes 350 is utilized to form a covalent bond with a compoundto be described later to generate a covalent bond layer 357.

Next, a step of bonding a predetermined compound to a surface of asubstrate having a plurality of assembly electrodes is carried out. Thesubstrate can be further provided with a dielectric layer covering theassembly electrodes, and partition walls, in addition to the assemblyelectrodes. The predetermined compound is not bonded to the surfaces ofthe assembly electrodes, but to surfaces of the partition walls and asurface of the dielectric layer surface exposed to outside.

In one embodiment, referring to FIG. 11, the substrate 161 is immersedor submerged in a solution that 0.01 to 1.0 M of THPP (see ChemicalFormula 3 below) is dissolved in EtOH (99.5%), and then in a solutionthat 0.01 to 1.0 M of SATES (see Chemical Formula 4 below) is dissolvedin EtOH (99.5%). Thereafter, the substrate is exposed to a temperatureranging from room temperature to 80° C. for 16 hours and then washedwith EtOH (99.5%). In this case, the hydroxyl group formed on thesurface of the substrate reacts with a silane group contained in THPP,and the hydroxyl group formed on the terminal of THPP reacts with asilane group contained in SATES. A Si—O bond is formed between thesubstrate 161′ and the compound.

In another embodiment, the substrate is submerged in a solution that0.01˜1.0M of SATES is dissolved in EtOH (99.5%). Thereafter, thesubstrate is exposed to a temperature ranging from room temperature to80° C. for 16 hours and then washed with EtOH (99.5%). In this instance,the hydroxyl group formed on the surface of the substrate reacts withthe silane group contained in SATES. A Si—O bond is formed between thesubstrate and the compound.

However, the compound is not limited to SATES and THPP, and can be acompound that contains a silane group capable of forming a Si—O bondwith a substrate and a functional group capable of forming a covalentbond with functional groups formed in the semiconductor light emittingdiode through heat treatment to be described later. For example, thecompound can be a compound containing a succinic anhydride group and asilane group.

Functional groups contained in the predetermined compound bonded to thesurface of the substrate are used to form covalent bonds with thesemiconductor light emitting diodes. Although the structure of thepredetermined compound partially changes according to the reactionbetween the compound and the functional groups formed on the surface ofthe substrate, such compound is referred to as a predetermined compoundin a state bonded to the surface of the substrate or the predeterminedcompound.

Thereafter, the self-assembly step described with reference to FIGS. 8Ato 8G is performed. Thereafter, heat treatment for the substrate iscarried out such that a covalent bond is formed through a reactionbetween the predetermined functional groups and the predeterminedcompound bonded to the surface of the substrate. A reaction between thesuccinic anhydride group contained in the predetermined compound and thepredetermined functional group can occur.

As illustrated in FIG. 12, when the predetermined functional group is ahydroxyl group, an ester bond is formed by the heat treatment. Thesuccinic anhydride group formed in the predetermined compound and thehydroxyl group form an ester bond through a chemical reaction asillustrated in FIG. 13.

On the other hand, as illustrated in FIG. 14, when the predeterminedfunctional group is an amine group, an amide bond is formed by the heattreatment. The succinic anhydride group formed in the predeterminedcompound and the amine group form an amide bond through a chemicalreaction as illustrated in FIG. 15.

A temperature of the heat treatment can vary depending on a type of thepredetermined functional group and a type of the predetermined compound,but preferably does not exceed 250° C. When the heat treatment isperformed at a temperature exceeding 250° C., the semiconductor lightemitting diodes can be damaged.

As a result of the heat treatment described above, a covalent bond layerforming a covalent bond with the dielectric layer and each of thesemiconductor light emitting diodes is formed. The covalent bond layerstrongly bonds the semiconductor light emitting diodes to the dielectriclayer, thereby preventing the semiconductor light emitting diodes frombeing separated from the substrate even when a voltage applied to theassembly electrodes is cut off after the self-assembly.

The use of the above-described covalent bond layer can result inpreventing different types of semiconductor light emitting diodes frombeing incorrectly assembled when sequentially self-assembling thedifferent types of semiconductor light emitting diodes. Hereinafter,utilizing the covalent bond layer when sequentially self-assemblingdifferent types of semiconductor light emitting diodes will bedescribed.

When sequentially self-assembling different types of semiconductor lightemitting diodes, a step of applying magnetic force to the semiconductorlight emitting diodes and a step of inducing or guiding thesemiconductor light emitting diodes to preset positions should beperformed more times than the number of types of semiconductor lightemitting diodes to be assembled.

For example, in the case of sequentially assembling the first to thirdsemiconductor light emitting diodes, each of the step of applying themagnetic force to the semiconductor light emitting diodes and the stepof inducing the semiconductor light emitting diodes to the presetpositions should be performed at least once in the state in which thefirst semiconductor light emitting diodes are introduced in the fluidchamber, at least once in the state in which the second semiconductorlight emitting diodes are introduced in the fluid chamber, and at leastonce in the state in which the third semiconductor light emitting diodesare introduced in the fluid chamber.

At this time, the assembly electrodes to which a voltage should beapplied vary depending on the type of semiconductor light emitting diodeintroduced in the fluid chamber.

Specifically, inducing the first semiconductor light emitting diodes tothe preset positions should be performed by applying a voltage to some(assembly electrodes belonging to the first group) of the plurality ofassembly electrodes such that the first semiconductor light emittingdiodes are induced to a first position, inducing the secondsemiconductor light emitting diodes to the preset position should beperformed by applying a voltage to some (assembly electrodes belongingto the second group) of the plurality of assembly electrodes such thatthe second semiconductor light emitting diodes are induced to a presetsecond position, and inducing the third semiconductor light emittingdiodes to the preset position should be performed by applying a voltageto some (assembly electrodes belonging to the third group) of theplurality of assembly electrodes such that the third semiconductor lightemitting diodes are induced to a preset third position.

Here, the heat treatment of the substrate is performed until theself-assembly for any one type of semiconductor light emitting diodes iscompleted.

Specifically, the heat treatment of the substrate should be performed atleast once in the state where the first semiconductor light emittingdiodes are seated at the preset first position, at least once in thestate where the second semiconductor light emitting diodes are seated atthe preset second position, and at least once in the state where thethird semiconductor light emitting diodes are seated at the preset thirdposition.

The heat treatment performed after the completion of the lastself-assembly is not essential, but is preferably performed even afterthe last self-assembly in order to prevent the semiconductor lightemitting diodes from being separated from the substrate during asubsequent process.

On the other hand, when self-assembly of another type of semiconductorlight emitting diodes is performed after completely self-assembling onetype of semiconductor light emitting diodes, a voltage applied to theassembly electrodes corresponding to the one type of semiconductor lightemitting diodes should be blocked.

For example, when the second semiconductor light emitting diodes areinduced to the preset second position after the first semiconductorlight emitting diodes are seated at the preset first position, a step ofblocking a voltage applied to a part (assembly electrodes belonging tothe first group) of the plurality of assembly electrodes can beperformed. This voltage blocking must be performed before theself-assembly with respect to the second semiconductor light emittingdiodes is performed.

In another example, when the third semiconductor light emitting diodesare induced to the preset third position after the first and secondsemiconductor light emitting diodes are seated at the preset first andsecond positions, a step of blocking a voltage applied to another part(assembly electrodes belonging to the second group) of the plurality ofassembly electrodes can be performed. At this time, the voltage appliedto the assembly electrodes belonging to the first group should be in ablocked state (i.e., should be blocked when self-assembling the secondsemiconductor light emitting diodes).

Accordingly, when semiconductor light emitting diodes of another typeare self-assembled after semiconductor light emitting diodes of one typeare self-assembled, the semiconductor light emitting diodes of the onetype cannot be separated from the substrate by virtue of the covalentbond layer, even if the voltage applied to the assembly electrodescorresponding to the semiconductor light emitting diodes of the one typeis blocked.

Table 1 below shows effects of the above-described heat treatment.Specifically, after performing the above heat treatment step, thesubstrate was kept in water for 1 hour while blocking the voltageapplied to the assembly electrodes. Thereafter, the number ofsemiconductor light emitting diodes left on the substrate wascalculated.

TABLE 1 SATES concentration (M) Reference: No 0.01 0.05 0.10 1.00 1.00THPP concentration (M) surface treatment — 0.50 Fixing maintenance rate(%): <10 59.6 85.8 94.2 97.8 99.5* Result after one-time immersion inwater Remarks Dielectric layer SiNx SiNx SiO₂ SiO₂ SiO₂ SiNx materialArea 6-inch assembly substrate (22500 sites) Surface treatment — Room40° temperature temperature

Referring to Table 1, it can be seen that a fixed rate of thesemiconductor light emitting diodes is equal to or higher than 99% whenheat treatment is performed by using both STATES and THPP. Accordingly,when semiconductor light emitting diodes of another type areself-assembled after semiconductor light emitting diodes of one type arecompletely self-assembled, a voltage applied to the assembly electrodescorresponding to the semiconductor light emitting diodes of the one typecan be blocked by use of the covalent bod layer.

As described above, the present disclosure can prevent another type ofsemiconductor light emitting diodes from being seated at a positionwhere one type of semiconductor light emitting diodes should be seated,in the case where different types of semiconductor light emitting diodesare sequentially self-assembled.

What is claimed is:
 1. A display device, comprising: a plurality ofsemiconductor light emitting diodes; first and second wiring electrodesrespectively extending from the plurality of semiconductor lightemitting diodes to supply an electrical signal to the plurality ofsemiconductor light emitting diodes; a plurality of pair electrodesdisposed on a substrate and having a first electrode and a secondelectrode that generate an electric field when a current is suppliedthereto; a dielectric layer disposed to cover the plurality of pairelectrodes; and a covalent bond layer disposed between the dielectriclayer and the plurality of semiconductor light emitting diodes, andforming a covalent bond with the dielectric layer and each of theplurality of semiconductor light emitting diodes, wherein the firstwiring electrode and the second wiring electrode are located at oppositesides of the plurality of pair electrodes based on the plurality ofsemiconductor light emitting diodes, and wherein the covalent bond layerbonds the plurality of semiconductor light emitting diodes to thedielectric layer when a voltage applied to the plurality of pairelectrodes for generating the electric field is cut off after theplurality of semiconductor light emitting diodes are assembled on thedielectric layer.
 2. The display device of claim 1, wherein an Si—O bondis formed between the dielectric layer and the covalent bond layer,wherein one of the plurality of semiconductor light emitting diodescomprises a first conductive semiconductor layer, a second conductivesemiconductor layer and an active layer placed between the first andsecond conductive semiconductor layers, and wherein the covalent bondlayer is disposed between only the first conductive semiconductor layerand the dielectric layer.
 3. The display device of claim 2, wherein anyone of an ester bond and an amide bond is formed between the pluralityof semiconductor light emitting diodes and the covalent bond layer. 4.The display device of claim 1, wherein the covalent bond layer is areaction product between a functional group formed on a surface of thesubstrate and a surface of each of the plurality of semiconductor lightemitting diodes, and a compound according to the following chemicalformula 3, or a reaction product between the functional group formed onthe surface of the substrate and the surface of each of the plurality ofsemiconductor light emitting diodes, and a mixture of the compoundaccording to the following chemical formula 3 and a compound accordingto the following chemical formula 4,


5. A display device, comprising: a plurality of semiconductor lightemitting diodes on a substrate; a plurality of pair electrodes disposedon the substrate and having a first electrode and a second electrodethat generate an electric field when a current is supplied thereto; adielectric layer disposed to cover the plurality of pair electrodes; anda covalent bond layer disposed between the dielectric layer and theplurality of semiconductor light emitting diodes, and forming a covalentbond with the dielectric layer and each of the plurality ofsemiconductor light emitting diodes, wherein the covalent bond layerbonds the plurality of semiconductor light emitting diodes to thedielectric layer when a voltage applied to the plurality of pairelectrodes for generating the electric field is cut off after theplurality of semiconductor light emitting diodes are assembled on thedielectric layer.
 6. The display device of claim 5, further comprisingfirst and second wiring electrodes respectively extending from theplurality of semiconductor light emitting diodes to supply an electricalsignal to the plurality of semiconductor light emitting diodes, whereinthe first wiring electrode and the second wiring electrode are locatedat opposite sides of the plurality of pair electrodes based on theplurality of semiconductor light emitting diodes.
 7. The display deviceof claim 5, wherein an Si—O bond is formed between the dielectric layerand the covalent bond layer, wherein one of the plurality ofsemiconductor light emitting diodes comprises a first conductivesemiconductor layer, a second conductive semiconductor layer and anactive layer placed between the first and second conductivesemiconductor layers, and wherein the covalent bond layer is disposedbetween only the first conductive semiconductor layer and the dielectriclayer.
 8. The display device of claim 7, wherein any one of an esterbond and an amide bond is formed between the plurality of semiconductorlight emitting diodes and the covalent bond layer.
 9. The display deviceof claim 5, wherein the covalent bond layer is a reaction productbetween a functional group formed on a surface of the substrate and asurface of each of the plurality of semiconductor light emitting diodes,and a compound according to the following chemical formula 3, or areaction product between the functional group formed on the surface ofthe substrate and the surface of each of the plurality of semiconductorlight emitting diodes, and a mixture of the compound according to thefollowing chemical formula 3 and a compound according to the followingchemical formula 4,


10. The display device of claim 5, wherein the covalent bond layer is areaction product between a functional group formed on a surface of thesubstrate and a surface of each of the plurality of semiconductor lightemitting diodes, and a compound containing a silane group capable offorming a Si—O bond with the substrate and the functional group capableof forming a covalent bond with functional groups formed on theplurality of semiconductor light emitting diode through heat treatment.11. The display device of claim 10, wherein the compound contains asuccinic anhydride group.
 12. The display device of claim 11, wherein,when the functional groups formed on the plurality of semiconductorlight emitting diode is a hydroxyl group, an ester bond is formed by theheat treatment.
 13. The display device of claim 12, wherein the succinicanhydride group and the hydroxyl group form the ester bond through achemical reaction.
 14. The display device of claim 11, wherein, when thefunctional groups formed on the plurality of semiconductor lightemitting diode is an amine group, an amide bond is formed by the heattreatment.
 15. A display device, comprising: a substrate; a plurality ofpair electrodes disposed on the substrate and having a first electrodeand a second electrode; a plurality of semiconductor light emittingdiodes on the plurality of pair electrodes; and a covalent bond layerdisposed between the substrate and the plurality of semiconductor lightemitting diodes, wherein the covalent bond layer bonds the plurality ofsemiconductor light emitting diodes to the substrate when a voltageapplied to the plurality of pair electrodes for generating the electricfield is cut off after the plurality of semiconductor light emittingdiodes are assembled on the substrate.
 16. The display device of claim15, further comprising a dielectric layer on the plurality of pairelectrodes, wherein the covalent bond layer is disposed between thedielectric layer and the plurality of semiconductor light emittingdiodes.
 17. The display device of claim 16, wherein an Si—O bond isformed between the dielectric layer and the covalent bond layer, whereinone of the plurality of semiconductor light emitting diodes comprises afirst conductive semiconductor layer, a second conductive semiconductorlayer and an active layer placed between the first and second conductivesemiconductor layers, and wherein the covalent bond layer is disposedbetween only the first conductive semiconductor layer and the dielectriclayer.
 18. The display device of claim 16, wherein any one of an esterbond and an amide bond is formed between the plurality of semiconductorlight emitting diodes and the covalent bond layer.
 19. The displaydevice of claim 15, wherein the covalent bond layer is a reactionproduct between a functional group formed on a surface of the substrateand a surface of each of the plurality of semiconductor light emittingdiodes, and a compound according to the following chemical formula 3,


20. The display device of claim 15, wherein the covalent bond layer is areaction product between a functional group formed on a surface of thesubstrate and a surface of each of the plurality of semiconductor lightemitting diodes, and a mixture of a compound according to the followingchemical formula 3 and a compound according to the following chemicalformula 4,